1. Field of the Invention
The present invention relates to a coating apparatus.
2. Description of the Related Art
As one technique of applying a coating material to a substrate such as a semiconductor wafer, a glass substrate or the like, a slit coating method is known. The slit coating method is a technique of applying the coating material onto the substrate by scanning a long slit nozzle having a discharge port in a slit shape.
Japanese Laid-open Patent Publication No. 2013-98371 discloses a slit nozzle that includes a retention chamber that retains a coating material and discharges the coating material filled in the retention chamber from a discharge port via a passage in a slit shape.
In the slit nozzle disclosed in the above publication, the liquid level of the coating material retained in the retention chamber lowers with progress of coating, so that the hydraulic head pressure of the coating material acting on the discharge port gradually decreases. When the hydraulic head pressure acting on the discharge port decreases, the amount of the coating material discharged from the discharge port decreases, causing possibility that the film thickness of a coating film to be formed on the substrate becomes non-uniform.
Here, in the technique discussed in the above publication, the liquid level height in the retention chamber is measured, and the pressure inside the retention chamber is linearly increased according to the lowering of the liquid level height so as to keep the discharge amount of the coating material constant.
However, there is room for further improvement in increasing the film thickness uniformity in the technique discussed in the above publication.